Pneumatic dryer ppt

Working principle and types of pneumatic Dryer

1. FOOD DEHYDRATION TECHNOLOGY (FT-403) PNEUMATIC DRYING OF FOODS PRESENTED BY : KRATIKA SINGHAM INT.FOOD TECHNOLOGY

2. CONTENTS INTRODUCTION WORKING PRINCIPLE FACTORS GOVERNING DRYING SPEED MECHANICAL FORCES MECHANISM OF WATER EVAPORATION FACTORS AFFECTING RESIDENCE TIME BLOCK DIAGRAM CONSTRUCTION TYPES ADVANTAGES & DISADVANTAGES APPLICATIONS LIMITATIONS EXPECTED NEW DEVELOPMENTS REFERENCES

3. Introduction Also known as “ flash drying ” Continuous convective process Indirect heating or direct firing Co-current flow High convective heat & mass transfer coeffient High drying rates & product quality Air velocity > free fall velocity of largest product Granular, crystalline, paste, powder, cake, flakes, gels, slurry Extension of fluidized bed drying Feeder - screw feeder, rotary valve, vibrating feeder, mixer Processes - pre-drying, drying & dehydration

4. SPECIFICATIONS Dried product size range = (10- 500)µm Short residence time = ( 0.5-10)sec Dried product( m.c ) = <=12% Throughput= few kg/ hr to several 100s tons/ hr Inlet air temp= (180-300˚c ) Incoming feed moisture= <40%( wb ) Bag filter pressure=(0.4- 0.6) Mpa

5. COMPONENTS H eater Wet material feeder Venturi Drying chamber Air Seperator (cyclone) Exhaust fan Dried product collector Dust seperator ex-( bag filters , electrostatic precipitators, wet scrubbers & fabric filters)

6. BLOCK DIAGRAM OF THE PNEUMATIC DRYER SYSTEM

7. PNEUMATIC DRYER

8. MECHANICAL FORCES Mechanical forces ( solid particle): D rag force (FD ) B uoyancy force (FB ) W eight force (FW ) of particle

9. MECHANISM OF WATER EVAPORATION 1. Convection heat transfer 2 . Heat conduction 3. Mass transfer ( granuels / particles to surface) 4 . Mass transfer(surface to drying air)

10. FACTORS GOVERNING THE SPEED OF DRYING 1. Moisture Dispersion 2. Temperature Differential 3. Agitation 4. Particle Structure 5. Particle Size

11. RESIDENCE TIME CAN BE ALTERED BY- Increasing the flash tube length Increasing holdup times in the product collection cyclone(s) Adding cyclones in series .

12. Cross-section Area of Pneumatic Dryer

13. CALCULATIONS

14. HEAT TRANSFER TOTAL HEAT REQUIREMENT DRYING TIME

15. FLASH DRYING SYSYTEM WITH RECIRCULATION OF EXHAUST GASES

16. FLASH DRYING SYSTEM WITH VENTURI

17. SPIN FLASH DRYER APPLICATIONS OF SPIN FLASH DRYER Extracting Wheat starch Soy protein Concentrated yeast

18. ROTARY FLASH DRYER Applications : soy protein , gelatinized starch

19. TWO STAGE PNEUMATIC DRYER WITH VAPOUR UTILIZATION

20. ADVANTAGES OF PNEUMATIC DRYING Short contact time and parallel flow make possible to dry thermolabile materials The dryer is easy to control. The low material content in the dryer enables equilibrium conditions to be reached very quickly. Due to small no. of moving parts ,the maintenance cost is low. Handle high flow rates.

21. DISADVANTAGES High efficiency gas cleaning system is required For lumped materials difficult to disperse There is a risk of fire and explosion Dryer cannot be used for toxic materials Less suitable for removal of internal moisture .

22. APPLICATIONS W heat sugar , gelatinized starch Powders like potato starch and corn starch Salt F lours B read crumps

23. (a) Corn gluten (b) caesin ( c) soup powder (d) vegetable protein ( e) spent tea (f) meat residues (g) bone meal

24. PACKAGING MATERIALS Powder products – Aluminium foil laminates , lined paperboards Meat products - HDP or polyamide-polyethylene-polyester-polyethylene laminated films. Fruits & veg pdt - paperboard folded cartons laminated with liner Flakes - foil laminated flexible pouches, friction lidded tins Cereals - cellophane plastic bag, LDP films

25. LIMITATIONS loss of power to the dryer will cause the product to fall out of suspension and build up in the dryer base & feed throat. If product hardens under heat ,it will cause blockage and require significant time to remove. Due to relatively high velocities, the particle size may be reduced (undesired) to attrition & impact. High velocities also may contribute to pre- mature component wear if system is not designated to inhibit it.

26. EXPECTED NEW DEVELOPMENTS IN FLASH DRYERS These developments are expected in the fields of: . Increased efficiency by heat recovery Applications of heat pumps in drying systems Efficient combined processes (hurdle technology) Development of models for overall systems ( mechanical dewatering, drying, heat recovery, powder collection, cooling stages )

27. REFERENCES Earle RL, unit operations in food processing, second edition, pergamon press, 1983, pg-85-89 Ramaswamy H, Marcotte M, Food Processing P rinciples and Applications, Taylor and francis , 2009, Pg - 233- 302 Kemp, I.C. and Oakley, D.E., Simulation and scale-up of pneumatic conveying and cascading rotary dryers, Drying Technology, 15(6–8 ),1699–1710 , 1997 Mindziul , Z. and Kmiec , A., Modelling gas–solid flow in a pneumatic-flash dryer, Drying Technology, 15(6–8), 1711–1720, 1997 Thorpe, G.R., Pneumatic Conveying Driers, Chemical Industry Development, Incorporating CP&E, 1975, pp. 13–19 Image source- internet Image source- internet